The invention relates to a process for the separation of hydrogen fluoride from its mixtures with 1-chloro-1, 1-difluoroethane, and more particularly, it relates to the separation of the unconverted hydrogen fluoride which is present in the mixtures resulting from the manufacture of 1-chloro-1, 1-difluoroethane by the hydrofluorination of chlorohydrocarbons. The present invention applies very particularly to the separation of the hydrogen fluoride present in the mixtures based on 1-chloro-1, 1-difluoroethane which results from the hydrofluorination of vinylidene chloride or 1,1,1-trichloroethane.
Most of the processes for the manufacture of 1-chloro-1, 1-difluoroethane by hydrofluorination give complex mixtures which contain, in particular, 1-chloro-1,1-difluoroethane and unconverted hydrogen fluoride. This applies to the process for the manufacture of 1-chloro-1,1-difluoroethane by the hydrofluorination of vinylidene chloride or 1,1,1-trichloroethane.
In order to separate pure 1-chloro-1,1-difluoroethane from these mixtures, they are commonly washed with an aqueous phase (British Pat. No. 1,323,234 filed on July 27, 1971 in the name of Daikin Kogyo Co. Ltd.) which can contain an acid or a base (Japanese Patent Application No. 47/39,086 filed on Aug. 31, 1964 in the name of Kureha Chemical Ind. Co. Ltd.)
These known processes exhibit the serious disadvantage that they recover the hydrogen fluoride in the form of aqueous solutions of inorganic fluorides or of hydrofluoric acid.
In fact, in order to obtain an adequate degree of conversion of the starting chlorohydrocarbon, it is necessary to employ, in the hydrofluorination, a large excess of hydrogen fluoride. It is highly desirable, for economic reasons, to recover the large excess of hydrogen fluoride in the anhydrous form so that it can be recycled into the reaction.
Simple distillation, which has already been proposed for the separation of mixtures of hydrogen fluoride with 1,1-dichloro-1-fluoroethane as described in U.S. Pat. No. 2,894,044 filed on Feb. 16, 1956 by Monsanto Chemical Co., cannot be employed for the purpose of recovering hydrogen fluoride in the anhydrous form, because hydrogen fluoride and 1-chloro-1,1-difluoroethane form an azeotrope. Furthermore, separation by decantation cannot be contemplated in view of the high mutual solubilities of hydrogen fluoride and 1-chloro-1,1-difluoroethane.